Conventional aircraft wing structures include sections which move pivotably for control purposes. Movable flaps on the leading edges of wings are particularly useful, providing a breaking force during landings. They can also be used to cause abrupt upward movement of the aircraft, which is especially useful for evasive military maneuvers.
Motors for driving such flaps cannot be mounted in the wings themselves because of size and weight considerations. The flaps are therefore driven, in the conventional arrangement, by a torque shaft that extends outwardly through the center of the wing structure from a motor mounted at the fuselage. So that this shaft can be of the lightest construction possible, it is driven at a relatively high rotational speed which is reduced by an actuator mounted in the wing that includes a reduction gear set, usually of the planetary type. Exemplary rotary actuators are shown in U.S. Pat. Nos. 3,640,150 to Leiner; 3,008,355 to Grudin; and 2,966,808 to Grudin.
Although these actuators are made as compact as possible and provide a ratio of input speed to output speed, they are nevertheless of substantial size when compared to the vertical dimension of an aircraft wing, particularly in the case of modern thin wing military fighter aircraft.
In recent years, wing thicknesses have decreased considerably, and have reached the point at which it is impossible to accommodate a rotary actuator of sufficient force transmitting capacity without creating a bulge on the wing profile. Any such disruption of the wing profile would be highly undesirable for aerodynamic reasons.
One partial solution to this problem has been the use of a series of smaller and smaller rotary actuators progressing toward the wing tip. As the size of the actuators decreases, their capacity falls off rapidly and larger numbers of actuators are required. This concept has its limits, however, and a point is reached at which actuators of a useful size cannot be accommodated within the wing. Moreover, there is a very significant increase in cost as the size of the individual actuators is decreased and their number is increased.
The outermost portion of a movable wing flap, nearest the wing tip, often is supported by the inner portion of that flap since it cannot be attached to an actuator. It may therefore be deflected by the air pressure through a disproportionate angle. This deflection may be more pronounced in the home position or in the activated position. The result is a loss of the aerodynamic efficiency of the flap and a reduction in the preciseness of the control of the aircraft that is achievable.
It is an objective of the present invention to provide an arrangement for driving movable wing sections that can be accommodated within a relatively thin wing profile without disrupting the airflow over the wing to a greater extent than necessary. A further objective is to permit precise control of a movable wing section, particularly at the thinnest portion of the wing, without increasing the number of actuators or increasing the cost of the driving mechanism.